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Alternating magnetic field detector out of an LED bar driver

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Someone Electro

New Member
I got an LED bar dB meter and riped its chip out.It was an KA2281 LED bar driver chip.And its to the bredbord for some experementing.

So i asembald it on an bredbord as shown in the datashet ( https://www.datasheetarchive.com/download.php?pi=48192 ) as i spoted from the datashet the biger the resistance betwen pin 1 and 2 or 16 and 15 the biger the gain so in the end an 1 Mohm resistor ended up in the bredbord.

Then i was conecting all sorts of stuf to it:a speaker ,piezo trnsducer... But wen i conected and secondary form an 220V to 6V transformer the bar has sudenly lit it self.Then o found that the elecrtomagnetic waves in generated in my monitor (in front of me so i cod se the datashet)ware being piked op by the coil.

Then i got the idea to use it as an in wall wire seker.So i thurned on the light and put the coil above the switch and herika it worked

But the problem is the first two leds keep lit proboly becose of radio waves being picked up by the wery sensetive preamp

I never wod of thogt that an LED bar driver chip wod make an alternating magnetic field detector (the cool thing is that it displays the strenth to) :D
 

Someone Electro

New Member
thats waht hapends if you get bored.

I now also put in green,yelow and red leds to make look beter

I wonder why my 220V to 15 V (at 10A :twisted: ) Transformer bidt work good as the coil.

I stil dont understand that 1 bar mono mode of this chip

To bad i dont have an 10 Mohm resistor around (meaby tha capacitance of the breadbord wod be to big to make it super senitive)

To bad i dont have an spare TV to take a part (man i cod get some good stuf from it)(An HV transformer wod be usefor in my stun gun)

wen ever i get an broken pese of electronic i take it a part.for exsamle i got this chip from an old transistor radio.I once got an tube radio but i found out it wasent much useful inside (and i lernd somting on high volteges the hard way)

and i got a time chip complete whith an 7 segment LED display out of an clock and i found out the the chip dosent fit in my breadbord.O that made me mad :evil: .

It wod be yust to good that bredbords wod have no capasitense (once it was enugh to triger my 555 timers reset pin)

Im planing to make an metal detector next time or an IR comunication

Hmm...I wonder if the LCD disoplay from an mobile phone cod be used for somting
 

zachtheterrible

Active Member
I wonder why my 220V to 15 V (at 10A ) Transformer bidt work good as the coil.

i would imagine cuz a coil stores all the energy in an electrical field and a transformer's secondary absorbs the energy that is radiated by the primary
 

zachtheterrible

Active Member
one thing u could do is this:
make a little inductor and put a 9v across it and see how far out the magnetic field reaches. then disconnect it and see how long the field stays. ive always been curiouis bout that
 

chemelec

Well-Known Member
Interesting Chip, But its not as sensitive as an LM3914
 

Someone Electro

New Member
Well the chip has built in 2 op amps as preamplefiers.So sure there not realy sesitive becose these not ment to be sensitive.To bad i dont have any op amps laying around.

I also put an trasnfromers iron core in the coil (The coil it self was riped out of an litle mains transformer) and it works good

By the way timing an electric field wod recuire a more suficent circuit.Becose of the input cap.It may dicharge slowly (Holding the led bar high) or the negative spike cod dicharge it intantly (Puling the LED bar low)

I think the AC filter works by discharging the cap thru the chip.

I tryed to put an 555 timer on and the piezo speaker.But the freqency tricked the AC filter.And the capacitense was mesing whith the timer chip.

If i wod conect an coil to a batery i wod only get the on and off spike (my device can only sense AC felds)I wod need to conected to AC.And the results wod be difrent from coil to coil (curent,inductance,size...)

But the bigest problem is its picking up radio waves and there fore limiting its sesetivety
 

Someone Electro

New Member
Heurica. By making 2 Mohm resitance betwen pin 1,2 and the positive its 2 times more sensitive and only the first LED is remaining on.

I tock a photo of it. I plugd in an bulky mains transformer on the table (15cm from it) so that all the leds got on.On the right is the primary coil of an transfromer whith its iron core (The devices sensor)
 

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